1. Field of the Invention
This invention relates to endoscopic surgical instruments. More particularly, this invention relates to an endoscopic forceps having a rack and pinion actuator handle and a track guided end effector assembly.
2. State of the Art
Endoscopic forceps are well known in the art. These instruments typically include a tube member and a control member extending through the tube member. The proximal end of the control member is typically coupled to an actuator handle which imparts reciprocal movement to the control member relative to the tube member. The distal end of the tube member is typically coupled to a clevis and a pair of forceps end effectors are pivotally mounted in the clevis. The distal end of the control member is coupled to the end effectors and reciprocal movement of the control member relative to the tube member causes the end effectors to pivot relative to the clevis and thereby open or close relative to each other. The tube member and the control member may be either rigid or flexible and the length of these members will vary, depending on the application, from several inches to several feet.
Several different kinds of actuator mechanisms are known for use with endoscopic forceps, including a handle-lever gripping member arrangement, and a thumb ring-spool type device. The handle-lever arrangement includes a stationary handle and a movable lever which is pivotally coupled to the stationary handle. The stationary handle has a distal finger ring and the movable lever has a proximal thumb ring. The stationary handle is coupled to the tube member and the movable lever is coupled to the control member. Typically, the handle-lever mechanism is held like a pair of scissors. Squeezing the thumb ring towards the finger ring pulls the control member in a proximal direction which usually results in closing the end effectors. The thumb ring-spool devices usually include a central slotted shaft having a proximal thumb ring, where the displaceable spool is slidable along the shaft and has a cross member which passes through the slot in the shaft. The tube member is coupled to the shaft and the control member is coupled to the cross member of the spool. The thumb ring-spool device is held like a hypodermic syringe. Squeezing the spool towards the thumb ring usually results in closing the end effectors.
Various designs for the clevis and end effectors are also known, although the clevis is most often a U-shaped member having an axle pin on which a pair of end effectors is pivotally mounted. The end effectors may be cutters or grippers. In the case of biopsy forceps, the end effectors are typically formed to be cuplike for holding a tissue sample which is cut or torn by the forceps.
There are many concerns in the design and manufacture of endoscopic forceps and these concerns are often related to the competing interests of strength versus cost of manufacture. The materials used in most endoscopic instruments include stainless steel and aluminum. More recently, in disposable instruments, plastic and bronze have been used. Manufacturing processes include molding, casting and extrusion. Typically, the end effectors are the most difficult part of the endoscopic instrument to manufacture because of their small size and because they must be strong. In cutting and biopsy instruments, the coupling of the end effectors to the clevis, the clevis to the tube member, and the end effectors to the control member raise additional strength considerations since the amount of force required to cut and/or obtain a biopsy tissue sample is relatively high. In addition, clogging of the clevis and the tube is always a consideration since various fluids and tissues may enter the clevis space and hamper operation of the forceps.
While the handle actuator is usually easy to manufacture, due in part to its relatively large size compared to the end effectors and the clevis, there are several considerations which must be addressed regarding the actuator handle. Among these considerations are smooth action, tactile feedback, and linear motion. These considerations are also often related to the clevis and end effector assembly insofar as the end effectors should move positively and smoothly in response to the movement of the actuator handle and the actuator handle should provide tactile feedback in response to the action of the end effectors. The amount of movement of the handle actuator needed to open and close the end effectors is also an important consideration.